1. Field of the Invention
In the processing of petroleum distillates, the presence of paraffins is often undesirable. For example, when a distillate is hydrocracked, the paraffins will be cracked in significant and undesirable amounts to light paraffinic gases, which are usually burned or used as LPG fuels and which are not useful for further processing.
Because the losses to relatively low profit gases are significant, there is a continuing search for methods of dewaxing petroleum distillates by processes yielding chemical products which are amenable to further processing to more profitable products.
We have discovered that under certain processing conditions ZSM-5-type zeolites can be used to dewax, or to remove paraffins, from petroleum feedstocks by forming C.sub.3 -C.sub.4 olefins which are valuable chemicals amenable to further processing steps; further, the residual uncracked material has improved characteristics useful for reforming operations to make gasoline.
These benefits are achieved through a process which uses a ZSM-5-type catalyst in a matrix substantially free of hydrocarbon cracking activity with a low nitrogen feedstock. Additionally, the process of this invention is particularly useful because the coking and deactivation rate of the catalyst composite is exceptionally low leading to greater efficiency in refinery operations. Further, the process can be practiced at any stage of hydrocarbon processing where it is desired to remove normal or slightly branched paraffins without detrimentally affecting the other chemical components of a feed.
2. Background Art
Dewaxing of virgin petroleum distillates using a ZSM-5 catalyst is known in the literature (see, for example, U.S. Pat. Nos. 3,894,939--W. E. Garwood--and 4,067,797--N. Y. Chen et al). However, these known processes suffer from disadvantages, including (1) high catalyst fouling or deactivating rates and (2) little or none of the C.sub.3 -C.sub.4 product fraction is C.sub.3 -C.sub.4 olefins.
U.S. Pat. No. 3,758,403, Rosinski et al, Sept. 11, 1973, discloses the catalytic cracking of hydrocarbons with mixtures of ZSM-5 and other zeolite catalysts under cracking conditions.
It is an object of this invention to provide a novel process for carrying out the catalytic upgrading of petroleum distillates in a more effective and efficient manner.
It is an object of this invention to provide a process in which at least a substantial portion of the product produced by catalytically dewaxing a distillate using a ZSM-5-type zeolite is a C.sub.3 -C.sub.4 olefin fraction.
Other and additional objects of this invention will be clear from a consideration of the complete specification including the claims thereof.